Rotation angle detection device

Abstract

A rotation angle detection device for detecting a rotation angle of a rotating body includes a magnet having poles arranged along a radial direction perpendicular to a rotation axis of the rotating body, the magnet being disposed to rotate together with the rotating body, a magnetic portion provided in a ring shape radially outward of the magnet, a plurality of gaps being formed in the magnetic portion at a plurality of locations along a circumferential direction, and a magnetic detection unit arranged in a particular gap of the plurality of gaps, the magnetic detection unit being configured to detect a tangential magnetic flux component in a tangential direction and a radial magnetic flux component in the radial direction of a magnetic field.

The invention claimed is: 
     
       1. A rotation angle detection device for detecting a rotation angle of a rotating body, comprising:
 a magnet having poles arranged along a radial direction perpendicular to a rotation axis of the rotating body, the magnet being disposed to rotate together with the rotating body; 
 a magnetic portion provided in a ring shape radially outward of the magnet, a plurality of gaps being formed in the magnetic portion at a plurality of locations along a circumferential direction; and 
 a magnetic detection unit arranged in a particular gap of the plurality of gaps, the magnetic detection unit being configured to detect a tangential magnetic flux component in a tangential direction and a radial magnetic flux component in the radial direction of a magnetic field, wherein 
 a ratio between a detection sensitivity of the tangential magnetic flux component and a detection sensitivity of the radial magnetic flux component by the magnetic detection unit is defined as a sensitivity ratio, 
 a ratio between a maximum value of the tangential magnetic flux component of the magnetic field and a maximum value of the radial magnetic flux component at the location of the magnetic detection unit is defined as a magnetic flux component ratio, and 
 a radial distance between the magnetic detection unit and the magnet is adjusted such that the difference between the magnetic flux component ratio and the inverse of the sensitivity ratio is smaller as compared to when the magnetic detection unit is located at the radial center of the particular gap. 
 
     
     
       2. The rotation angle detection device according to  claim 1 , wherein
 the magnetic detection unit includes
 a horizontal Hall element that detects the radial magnetic flux component of the magnetic field, and 
 a vertical Hall element that detects the tangential magnetic flux component of the magnetic field, and 
 the vertical Hall element has a lower sensitivity than the horizontal Hall element. 
 
 
     
     
       3. The rotation angle detection device according to  claim 1 , wherein the radial distance between the magnetic detection unit and the magnet is adjusted such that the magnetic flux component ratio is equal to the inverse of the sensitivity ratio. 
     
     
       4. The rotation angle detection device according to  claim 1 , wherein
 a minimum width in the tangential direction necessary for providing the magnetic detection unit is defined as a minimum required width, and 
 a tangential width of the particular gap is adjusted such that the difference between the magnetic flux component ratio and the inverse ratio of the sensitivity ratio is smaller as compared to when the tangential width of the particular gap is the minimum required width. 
 
     
     
       5. The rotation angle detection device according to  claim 4 , wherein the tangential width of the particular gap is adjusted such that the magnetic flux component ratio is equal to the inverse of the sensitivity ratio.